Combination control and reference circuit for a magnetic amplifier



July 3, 1956 E. T. HOOPER, JR 2,753,517 COMBINATION CONTROL ANDREFERENCE CIRCUIT FOR A MAGNETIC AMPLIFIER Filed March 27, 1953 7OCONTROL 68 SIGNAL VA\ A -7a -4e; '86 INVENTOR 92 $90 EDWARD T HOOPER,JR.A A I- 96 v 94 BY RN, Hfl QkQ ATTORNEYS COMBINATION CONTRGL ANDREFERENCE CIRCUIT FOR A MAGNETIC AMPLIFIER Edward T. Hooper, Jr.,Hyattsville, Md., assignor to the United States of America asrepresented by the Secre= tary of the Navy Application March 27, 1953,Serial No. 345,271

7 Claims. (Cl. 323--89) (Granted under Title 35, U. S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to magnetic amplifiers and more particularlypertains to a combination bias and control circuit therefor.

In magnetic amplifiers, the reactance of the cores and hence the currentflow through the controlled windings thereon is varied by the passage ofa control current through the control winding on the core. The properoperating flux level in the cores is established by bias circuits, whichbias circuits commonly utilize separate bias windings on the cores whichare energized from the power supply source.

in half-wave self-saturating magnetic amplifiers it is desirable toutilize half-wave currents for both biasing and control. The presentinvention is a continuation-inpart of the copending application ofEdward T. Hooper, Serial No. 335,619, filed February 6, 1953, forFull-Wave Magnetic Amplifier. The control circuit provides a halfwavereference voltage from an A. C. supply source, and a half-wave controlvoltage from an A. C. control source, both control and referencevoltages being placed on the saturable reactor core in a single winding.

An important object of this invention is to provide a circuit forapplying half-wave control and reference voltages in a single winding onthe reactor core.

Another object of this invention is to provide a circuit for providing ahalf-wave reference from an A. C. supply source and a half-wave controlvoltage from an A. C. control source and for applying the control andreference voltages to a single winding on the reactor.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. 1 is a schematic diagram of the combination reference and controlcircuit applied to the bridge type halfwave magnetic amplifier; and

Fig. 2 is a schematic diagram of a modified form of combination bias andcontrol circuit having a second amplifier stage connected in cascadetherewith.

Reference is now made more specifically to Fig. l of the drawingswherein there is illustrated a half-wave bridge type magnetic amplifierhaving a combination bias and control circuit applied thereto. Theamplifier includes a pair of cores 10 and 12 of saturable magneticmaterial. The core 10 has split load windings 14 and 16 thereon, thecore 12 having split load windings 18 and 2d wound therein. Loadwindings 14 and 18 are connected in series circuit with rectifiers 22and 24 across the A. C. supply source 26 and constitute one pair ofadjacent legs of a bridge circuit, the load windings 16 and 20 beingconnected in series circuit with rectifiers 28 and 30 across the supplysource 26 and forming the other pair of adjacent legs of the bridgecircuit. The load 32 is connected nited States Patent C 'ice to a pointbetween the rectifiers 22 and 24, and between the rectifiers 28 and 30.

The circuit thus far described is conventional, and forms no part ofthis invention. In operation, during onehalf cycle of the A. C. powersupply voltage 26, current flows through winding 14, rectifier 22, andin one direction through load 32, through rectifier 28, and winding 16,the load current also flowing during the same half cycle through winding20, rectifier 30, through load 32 in the opposite direction, throughrectifier 24 and winding 18. The parameters of the circuit are adjustedso that when the reactances of the cores it) and 12 are equal, the loadcurrents flowing through the load windings on each of the cores areequal, and consequently the resultant current flowing through the load32 is zero. However, when the reactances of the cores are varieddifferentially, a resultant load current flows through load 32 in adirection dependent upon the sense of the unbalance of the cores.

The combination bias and control circuit includes a transformer 34, theprimary 36 of which is connected across the A. C. power supply source26. The transformer 34 has a center-tapped secondary 38, whichcenter-tapped secondary constitutes one pair of adjacent legs of thecontrol bridge circuit. The third leg of the control bridge circuitincludes resistor it), rectifier 42, and corn trol winding on the core12. The fourth leg of the bridge includes resistor 46, rectifier 5t andcontrol winding 52 on the core 10. A balancing potentiometer 46 may beprovided to facilitate equalizing the current flow through the controlwindings 44 and 52 under zero control signal conditions. The controlsignal source 54 is connected between the tap on the secondary 38 andthe tap on the potentiometer 46. Rectifiers 42 and 50 are polarized sothat current flows through the control windings 4-4 and 52 during thenon-conducting half cycle of the half-wave bridge circuit comprisingwindings 14, it 18 and 26 previously described. Resistors 4t) and 48 andpotentiometer 46 are adjusted so that the half-wave currents flowingthrough windings 44 and 52 preset the desired operating flux level inthe cores 10 and 12. When a control signal from the control source 54 isapplied, the combination reference and control circuit bridge isunbalanced causing an increase in current flow through one of thecontrol windings and a decrease in current flow through the othercontrol winding. These combined actions take place on the half-cyclewhen the load windings on the cores 1t) and 12 are non-conducting,whereby the flux levels of the respective cores are preset to the propervalue determined by the control signal to thereby determine the firingangle of the cores on the succeeding half-cycle.

As is deemed apparent, the combination control and reference bridgecircuit provides a half-wave reference current from the A.- C. powersupply source, and in addition effects half-wave control from an A. C.control source.

In the embodiment illustrated in Fig. 2 of the drawings, the combinationcontrol and reference circuit includes a center-tapped impedance havinglegs 60 and 62, which impedance may be the inductance illustrated or,alternatively, may comprise a capacitive or resistive impedance. Thelegs 60 and 62 of the center-tapped inductance form one pair of adjacentlegs of a bridge circuit, rectifiers 64 and 66, resistors 63 and 70,windings 72 and 74 on saturable reactor cores 76 and 78 respectively andthe potentiometer 80 forming the other pair of adjacent legs of thebridge circuit. Potential from the A. C. power supply source 82 isapplied across the legs 60 and 62 of the center-tapped inductance, andthe rectifiers 6 and 66 are phased so as to allow current flow throughthe control windings 72 and 74 of the bridge only in one to a pointdirection. This permits a constant half-wave reference voltage to beapplied to the control windings, which voltage is adjusted to the propervalue by the resistors 68 and 70. The control signal from the source 84is applied between the tap on the center-tapped impedance and the tap onthe potentiometer 89, the potentiometer being. provided to permitbalancing of the bridge circuit under zero control signal conditions.When the bridge is balanced, the same reference voltage appears on bothcontrol windings 72 and '74. The application of a control signal,however, unbalances the bridge circuit, raising the voltage on onecontrol winding and lowering the voltage on the other.

Load windings 86 and 88 on cores '76 and 78 respectively are connectedin a bridge circuit, and form one pair of adjacent legs thereof. Theremaining pair of legs of the bridge are formed by rectifiers S t) and92 and the control windings 94 and 96 on the cores 95 and 100, whichlast mentioned pair of cores constitute a portion of a second stage ofthe magnetic amplifier. Load windings as and 3% are energized, as fromthe supply source 82 and the rectifiers 9t) and 92 are phased so thatload current flows through the load windings during the half-cycle ofthe power supply voltage succeeding that half-cycle during whichreference flux is established in the cores 76 and 78. The second stageload circuit [not illustrated] may be of any desired type such as thehalf-wave bridge type illus trated in connection with Fig. l of thedrawings.

From the foregoing it is deemed apparent that the combination bias andcontrol circuit supplies both a halfwave reference voltage and ahalf-wave control voltage to a single control winding on each of thereactors. The half-wave reference potential may be supplied from an A.C. power supply source and the control voltage supplied by either an A.C. or a D. C. control source.

The voltages induced in the control windings on each of the cores areadditive and only under zero control signal conditions will there be noinduced current flow through the control signal source. With a controlsignal, an unbalance occurs and a small induced current flows throughthe control source. This is true of all two-core control systems, but inthe instant case the induced current does not flow on the half-cycleduring which control is being formed, and no error results.

It is deemed apparent that the A. C. control signal source and the A. C.supply source may be interchanged in the control bridge circuit providedone of the rectifiers in the control bridge circuit is reversed so thatthe reference or bias current only flows during one half-cycle of the A.C. supply voltage. However. the bridge circuit including power windings14, i5, and Eli must be energized from a power supply source. Thus, thepower supply voltage as from source 2 6 may he applied between the tapon transformer secondary winding 32 and the tap on potentiometer 46, inwhich case the control voltage from source 54 would be applied acrosstransformer primary winding 36. However, one of the rectifiers such as42 must be reversed so that the reference or bias current llows duringone half-cycle of the power supply voltage.

Obviously many modifications and variations of the present invention arepossible in the light of the a oof/e teachings. it is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent is:

l. in a half-wave self-saturating type magnetic amplifier including apair of saturable reactor cores each having controlled winding meansenergized from an A. C. source on the same alternate half-cycles of saidsource. a combined bridge type bias and control circuit including acontrol winding for each of said cores interconnected to be included inone pair of adjacent legs of the bridge, impedance elements seriallyinterconnected with said control winding to form the other pair ofadjacent legs of 4 the bridge, circuit means for applying said A. C.source across one pair of diagonally opposite terminals of the bridge,unidirectional impedance elements in said bridge circuit for passingcurrent from said source in one direction only through the bridge sothat half wave current flows through the control windings only duringthe other alternate half-cycles'of said source, and means for applying acontrol signal across the other pair of diagonally opposite terminals ofthe bridge to thereby differentially vary the half-cycle current flowthrough the control windings.

2. In a half-wave magnetic amplifier, a pair of cores of magneticmaterial having definite saturation characteristics, a control winding;on' each of said cores, a control signal source, means connecting saidcontrol windings to said control source in separate parallel branchcircuits, an impedance element in each of said branch circuits, supplyvoltage means for applying an A. C. potential across said impedanceelements, and unidirectional impedance elements in each of said branchcircuits connected so that current from said supply voltage means flowsin the same direction through said branch circuits only during the samealternate half-cycles of the supply voltage means.

3. The combination of claim 2 including means in each of said branchcircuits for adjusting the magnitude of the half-wave currents flowingtherethrough.

4. A bridge circuit energized from a biasing source and a control signalsource. for functioning simultaneously as a bias circuit and a control.circuit for a magnetic amplifier having a plurality of saturable corereactors with power windings wound thereon, saidbridge circuit beingdefined by a closed series loop including control windings forpresetting, the flux levels in predetermined ones of said reactors in amanner'correlative to the current flowing through said control windingsas a consequence of application thereto of a biasing voltage and acontrol voltage from said biasing source and said control signal source,respectively, and unidirectional conductive means for permitting currentflow through said series loop in one direction only.

5. The bridge circuit of claim 4, wherein said bridge has two pairsofdiagonally opposite terminals, and further including circuitconnections for. connecting said control signal source across one ofsaidpairs of diagonally opposite terminals, and circuitv means forapplying biasing voltage from said biasing: source across the other pairof diagonally opposite. terminals.

6. A bridge: circuit according to: claim 5 to serve as a common bias andcontrol circuit for a half-Wave magnetic amplifier having a pair ofsaturable core reactors with power windings arranged to be energizedonly on the same alternate half-cycles from. an A. C. source, whereinsaid. unidirectional conductive means are so poled that said currentflow through said series loop occurs only during the nonconductivehalf-cycles of said power windmgs.

7. A half-wave magnetic amplifier having a common bias and controlcircuit comprising, in combination, a source of alternating current; apair of saturable core reactors; load windings on said reactorsconnected across said source through rectifier means arranged to-passcurrent. through said load windings only during the same alternatehalf-cycles of said source; a control winding on each of said cores andserially interconnected to define a first common terminal at thejunction thereof; a pair of impedances' serially interconnected todefine a second common. terminal at the junction thereof; a firstunilateralv conductive device electrically interposed between one' ofsaid. control windings and one of said impedances and serially connectedto the unconnected terminals of said one control winding and said oneimpedance, and a second unilateral conductive device elec tricallyinterposed between the other of said control windings and the other ofsaidirnpedances and serially con nected to the unconnected terminals ofsaid other control winding and said other impedance to thereby form adirection through said series loop only during the nonclosed series loopincluding said pairs of control Windconductive half-cycles of said loadwindings.

ings and impedances, and said first and second unilateral conductivedevices; a control signal source connected References Cited in the fileof this patent across said first and second common terminals; and cir- 5UNITED STATES PATENTS cu1t means for applying an alternating currentfrom said alternating current source across said pair of impedances,2,632,145 Sikorra Mar. 17, 1953 said unilateral conductive devices beingpoled so as to 2,677,099 Rau Apr. 27, 1954 pass current from saidalternating current source in one 2,704,823 Storm Mar. 22, 1955

